1. Field of the Invention
The present invention relates to a transmission line for transmitting RF signals such as microwave signals and EHF signals. Further, the present invention relates to a transceiver including the transmission line, such as a radar system and a communication device.
2. Description of the Related Art
Generally, a waveguide transmission line using a dielectric substrate includes, for example, two rows of through holes formed on the dielectric substrate for connecting two or more conductive layers formed on the dielectric substrate (as disclosed in Japanese Unexamined Patent Application Publication No. 2000-196301 or the like). Further, such a transmission line includes a coupler formed by making an opening in the conductive layer on the top surface of the dielectric substrate and a square waveguide that is formed around the coupler and is connected to the coupler. In such a case, a waveguide is formed between the two rows of through holes. Further, the waveguide in the dielectric substrate and the square waveguide are connected via the coupler.
In the above-described case, only the through holes are used as current paths formed along a direction perpendicular to the waveguide (the thickness direction of the dielectric substrate). Therefore, as RF signals are propagated, a flowing current is concentrated into the through holes. Subsequently, the conductor loss is increased as the current density in the through holes is increased.
Further, if a semiconductor element such as a Microwave Monolithic Integrated Circuit (MMIC) were mounted on the top surface of the dielectric substrate, the connectivity between the semiconductor element and the above-described waveguide and square waveguide would be low. Therefore, the losses at connection points would be large.